This application claims priority from Japanese Application 2001-001,149, filed Jan. 9, 2001, the entirety of which is incorporated herein by reference.
1. Field of the invention
This invention relates to a semiconductor light-emitting element, particularly usable for a white color light-emitting diode.
2. Related Art Statement
Recently, various light-emitting diodes (LEDs) are widely available. LEDs are expected for illuminating use as well as displaying use because of their low electric power consumption, long life time, CO2 gas reduction originated from the reduction of the high energy consumption such as the low electric power consumption, and thus, much demand for the LEDs are expected.
As of now, the LEDs are made of various semiconducting materials such as GaAs-based semiconducting material, AlGaAs-based semiconducting material, GaP-based semiconducting material, GaAsP-based semiconducting material and InGaAlP-based semiconducting material, and thus, can emit various color lights from red to yellow-green. Therefore, the LEDs are employed particularly for various displaying use. Recently, blue and green LEDs have been realized by using GaN-based semiconducting materials. As a result, selecting a given LED, a given color light from red to blue, that is, within visible light range, can be obtained from the LED, and full-color displaying is also realized. Moreover, white color light-emitting diodes (white color LEDs) are being realized by using RGB LED chips or using two color light-emitting diodes composed of blue LEDs with a yellow fluorescent substance thereon. As a result, LED illumination is being realized at present.
However, the white color LED using the ROB LED chips requires higher cost because the plural LED chips are employed, so that in view of the cost, it is difficult to realize the white color LED for illumination use. On the other hand, full color can not be recognized by the white color LED using the two color light-emitting diode because it employs only two primary colors, instead of three primary colors. Moreover, in the white color LED, the brightness of only about 25 lm/W can be realized, which is very small as compared with the brightness of 90 lm/W of a fluorescent tube.
Therefore, a white color LED employing three primary colors is strongly desired because of the low energy consumption taking environmental problems into consideration. In reality, such a white color LED is intensely developed by Japanese national projects and foreign major electric-nanufacturing enterprises.
It is an object of the present invention to provide a new semiconductor light-emitting element preferably usable for a LED to emit an any color light, particularly a white color LED. Herein, the wording xe2x80x9cLEDxe2x80x9d means all kinds of semiconductor light-emitting elements, including a PN-junction light-emitting element.
For achieving the above object, this invention relates to a semiconductor light-emitting element including a substrate and an underlayer formed on the substrate. The underlayer is made of a first semiconducting nitride material including at least Al element and has a crystallinity of 90 seconds or below in full width at half maximum of an X-ray rocking curve.
A light-emitting layer is formed on the underlayer and is made of a second semiconducting nitride material including at least one element selected from the group consisting of Al, Ga and In, and at least one element selected from rare earth metal elements.
A first electrode is a Schottky electrode and a second electrode is a Schottky electrode or an ohmic electrode, which are formed on the light-emitting layer.
The inventors intensely studied to obtain a semiconductor light-emitting element to emit a given color light, particularly a white color light. As a result, they discovered the following facts. That is, if, in a semiconductor light-emitting element including a substrate, an underlayer, a light-emitting layer, a first electrode made of a Schottky electrode and a second electrode made of a Schottky electrode or an ohmic electrode on the light-emitting layer; and the light-emitting layer is made of a semiconducting nitride material containing at least one element selected from the group consisting of Al, Ga, In, the crystallinity of the underlayer is developed, and a given rare earth metal element is incorporated in the light-emitting layer, the inherent color light originated from the rare earth metal is emitted from the light-emitting layer at a relatively large intensity.
In the abovementioned semiconductor light-emitting element, since a given rare earth metal element is incorporated into the light-emitting layer, the inherent color light originated from the rare earth metal element is emitted from the light-emitting layer when the light-emitting layer is excited by an electric current injected from the electrodes.
Therefore, by selecting a given element from rare earth metal group appropriately, a desired color light is emitted through the semiconductor light-emitting element. Moreover, if plural rare earth metal elements are selected appropriately, the inherent color lights originated from the respective rare earth metal elements are superimposed, and thus, a white color light can be generated at and emitted from the semiconductor light-emitting element.
In the present invention, such a rare earth metal element may be directly incorporated into the underlayer. In this case, the underlayer doubles as a light-emitting layer, and thus, the above-mentioned light-emitting layer separated from the underlayer may be omitted.